Objective measures of physical function have become important throughout healthcare. The applicants propose to develop a marketable "laboratory test" that provides a quantitative index of individual ambulatory function. The system will use a robust field instrument called the Step Activity Monitor (SAM) which has been extensively tested for accuracy, scientific validity, and durability in the field. The ultimate goal is to provide a sound, accessible system allowing users to efficiently obtain quantitative profiles that 1) reflect the ambulatory function of persons in their own normal environment, and 2) can be a readily interpreted clinical indicator. The proposed system will be attractive and useable across many fields to manage, analyze, report and interpret complex data about physical function in a clinically useful manner. Specific Aims of the Phase I are: 1. Definition of improved analysis methods for interpreting step count data. 2.Implementation of analysis methods as client/server based software system to allow remote data collection with centralized analysis and secure electronic transmission of reports. 3. Demonstration of usability by practitioners in a clinical setting. PROPOSED COMMERCIAL APPLICATION: The proposed system could become a standardized test for ambulatory function in many fields such as health, fitness and weight loss.